This project was terminated temporarily at the end of July 1999 when Dr. Allan left NIH for employment in the private sector. As yet, we have not published the results of Dr. Allans purification and characterization experiments dealing with the enzyme that catalyzes a substitution reaction in which selenium replaces sulfur in 2- thiouridines in tRNAs. Although selenophosphate clearly is the donor of selenium in this reaction, the exact nature of the enzyme complex that catalyzes the synthesis of 2-selenouridine in the tRNAs is not clear. The presence of ribosomal proteins detected by sequence analysis of isolated ribosomal proteins is of sufficient interest to warrant submission of the presently available data. - tRNA, selenium, nucleosides, nucleotides, modification, biosynthesis, T-cells, HeLa, 5- methylaminomethyl-2-selenouridine, eukaryotes